Negative pressure is a term used to describe a pressure that is below normal atmospheric pressure. At room temperature and at sea level, a defined volume of air contains molecules moving in random directions, and these moving molecules exert a force that is equal to the normal atmospheric pressure of approximately 756 mmHg (about 1 bar). Negative pressure has been achieved by removing air from an area of interest, for example at a wound site via a suction pump. Devices for the generation of topical negative pressure at the surface of a subject's skin have been used for many hundreds of years to treat humans. For example, the cupping technique, which relates to positioning a mouth of a rigid vessel containing hot air on a human's skin, is a well-known technique. Spring powered syringes and suction cups are other mechanical techniques that have been used for generating a vacuum on human tissue. In common with cupping, such other mechanical techniques have offered a limited topical negative pressure duration and little or no range of neutral to positive pressures. This is due to design constraints and that the cupping technique and other mechanical techniques are not self-contained and can hinder a user's mobility.
Known topical negative pressure devices range from cumbersome wrinkle reducing suction apparatuses to wound therapies that include fluid-permeable wound cavity filling elements, covering dressings, reasonably air-tight means for sealing against the skin, and drainage tubes connecting the wound site and cavity filling element to the vacuum source via a fluid collection canister. The mode of action of such devices is the application of negative pressure to the tissue site, causing an expansion of the enclosed tissue into the cavity enabled by sealing the apparatus against the skin. When the treated tissue site is a wound, exudate can be drawn from the surrounding tissue through the porous cavity filler, into the drainage tube and then into a remote collection receptacle. A consideration of such known devices is the ability of the wound cavity filler to remain sufficiently porous so that, when compressed under negative pressure, fluid may be transported from the tissue site to a drainage or aspirant tube.
To enable a more prolonged application of topical negative pressure, powered systems, which include a vacuum generation source such as a pump, have been developed and many examples of such systems are used today for skin treatments and restorative purposes like the temporary removal of wrinkles. Many of these systems, however, are not convenient for users. Such known systems can be large, heavy, noisy, uncomfortable, and not simple for users to apply and initiate a controlled pressure condition. Such known systems also rely on an outside power or vacuum source to create topical negative pressure conditions.
Such tissue treatment, surgery, and other advanced technical interventions are becoming more common given the occurrence of both the aging population, as well as increasingly compromised patient populations. This trend looks set to continue. In wound care, for example, healthcare professionals are now more likely to encounter wounds that are difficult to manage with complex healing problems. Attempts have been made to produce more simple mechanical devices able to apply topical and negative pressure to a tissue site. It will be appreciated that such a medical device, due to its relative simplicity of design, would be expected to reduce material costs and assembly costs. For example, attempts have been made to use a hand-pump system for the application of topical negative pressure at a tissue site. However, such a system fails to enable easier application by the user, discreet use, and prolonged convenient application of topical negative pressure, and, in fact, re-evacuation is often necessary. These can be serious deficiencies, particularly as many such systems are ideally useable for prolonged periods, such as overnight.